Active cable assemblies are gaining in popularity as a way of exploiting the broad bandwidth capability of optical fiber. As used herein, an active cable assembly is an optical cable in which the circuitry for converting between electrical and optical is on either side of the optical cable. Thus, the electrical to optical conversion is performed within the cable assembly itself. Significant performance improvements especially with respect to maximum cable length maybe achieved using an active cable assembly.
A critical component of an active cable assembly is the interposer, which optically couples an opto-electric device (OED) to a fiber in the cable assembly. Generally, although not necessarily, the axis of the OED and that of the fiber tend to be perpendicular. Thus, the interposer serves not only to optically couple the OED and the fiber, but also to bend the light to effect the coupling.
Referring to FIG. 12, a schematic of a state-of-art interposer 1200 is shown. An array of OEDs 1207 such as VCSELs or photodiodes is mounted to a substrate 1201. The OEDs in this embodiment are mounted on the side opposite surface 1201a of the substrate to which the interposer 1200 is connected. In such an embodiment, the substrate is optically transparent such that light is transmitted through the substrate. A typical substrate is a glass plate. The glass plate is relatively thin, for example, 0.5 mm thick. To effect optical coupling with the OEDs, the interposer comprises an array of lenses 1204. The lenses 1204 are defined by an air space 1211 between the lens surface and the glass plate. The reflective surface 1209 turns the light at 90 degrees between the lenses 1204 and the fiber 1210.
The interposer 1300 shown in FIG. 13 is an improvement to interposer 1200 in that it comprises a cavity 1330 for receiving a ferrule 1331 containing the optical fiber(s) 1332, rather than just the optical fiber as shown in FIG. 12. The fiber(s) 1332 are held in ferrule 1331 parallel to the substrate 1301. Modularizing the fiber assembly and making it discrete from the interconnection between the OEDs and the lenses of the interposer is a marked improvement over the prior art interposer 1200. In particular, the use of an independent ferrule 1331 allows the fiber assembly to be tested independently of the OED and interposer assembly. Therefore, if problems are detected in the termination of the fibers, the fiber assembly can be reworked rather than scrapping the entire assembly.
Although the interposer 1300 improves the manufacturability of the cable assembly interposer by allowing the cable assembly to be tested independently of the completed interposer, the interposer 1300 still has compound optical alignments as the receptacle must be precisely aligned with the lens in a common assembly. Therefore, Applicant has identified a need for a simpler interposer configuration which eliminates or reduces compound optical couplings. The present invention fulfills this need among others.